As exemplary techniques for forming thin films of semiconductor devices, CVD (chemical vapor deposition) methods are known. Where a capacitor is fabricated in a process of manufacturing a semiconductor device, it is required to form a dielectric thin film with a high dielectric constant and a low leakage current, which facilitates high integration of the device. In order to achieve this, a film formation technique employing an organic metal material as a source material is used to form the dielectric thin film.
In such a film formation technique, an organic metal material used as a source material is normally in a liquid state or liquefied by a suitable solvent. The source material is turned into mist and vaporized in a vaporizer (source material vaporizer), and is then supplied into the reaction chamber of a film formation apparatus. In the vaporizer, the organic metal material needs to be sufficiently vaporized at a temperature that does not cause decomposition of the material. However, in practice, non-vaporized residual mist may be generated, and/or decomposition products of the organic metal material may be generated as particles. Accordingly, a problem arises in that the mist and particles degrade the quality of a thin film formed within the reaction chamber.
In light of this problem, conventionally, such a vaporizer is known that includes a filter disposed at the outlet to remove mist and particles (for example, see Jpn. Pat. Appln. KOKAI Publications No. 7-94426 and No. 8-186103 and U.S. Pat. No. 6,210,485). Further, such a vaporizer is known that includes a vaporizing plate disposed at an angle perpendicular to or interfering with the flow path of a gas material, and a heater disposed in the vaporizing plate to promote vaporization (for example, see Pat. Appln. KOKAI Publication No. 6-310444).
Furthermore, such a vaporizer is known that includes a vaporizing surface disposed at a position opposite the spray direction of a source material within a vaporizing chamber and configured to be controlled in temperature independently of the other inner surface portions of the vaporizing chamber (for example, see Pat. Appln. KOKAI Publication No. 2002-110546, and particularly a structure shown in FIGS. 7 and 8 thereof). The vaporizing surface is set at a temperature higher than that of the other inner surface portions. In this respect, conventionally, when a source material is intensively sprayed on an inner surface portion opposite the spray direction of the source material, non-vaporized residuals may be generated due to a temperature decrease of the inner surface portion. In contrast, the improved vaporizer described above can reduce such non-vaporized residuals and thereby increase the vaporization rate.
However, in the conventional gas material supply system described above, a filter may be clogged with mist and particles. In this case, the conductance is decreased in a short time, and the pressure inside a vaporizer is thereby increased. This decreases the gas material feed rate and vaporization efficiency at the vaporizer. Accordingly, in order to maintain the gas material feed rate and vaporization efficiency, the filter requires frequent cleaning or replacement, which in return decreases the operation rate of the apparatus.
According to a conventional system employing the vaporizing plate with a heater disposed therein described above, the vaporizing plate needs to widely expand in a gas passage to increase the trapping rate of mist. In this case, the vaporization efficiency at a vaporizer is decreased. Further, it can be hardly expected that particles are trapped by the vaporizing plate.
Further, according to a conventional vaporizer with the vaporizing surface independently controllable in temperature described above, the temperature of an inner surface portion opposite the spray direction of a source material is independently controlled. With this arrangement, the vaporization efficiency of the source material is increased within a vaporizing chamber. However, this arrangement can hardly work on the mist out of contact with the vaporizing surface. Accordingly, when non-vaporized residuals and particles do not come into contact with the vaporizing surface, but flow directly to the outlet or gas lead-out port of the vaporizing chamber, they can be discharged as they are.